In a GC the fluid is in the form of gas. Samples of fluid under test are typically under the control of control devices such as pumps, valves, pressure transducers and pressure regulators. The control devices help in the acquisition of samples, and the isolation, handling and separation of the samples during the process of chemical analysis. In a GC, a sample aliquot is directed, either manually or automatically, through a complicated array of plumbing hardware and control systems that that perform various functions before the sample flows through one or more separation columns. In the separation columns different compounds in the sample fluid are isolated. As the isolated compounds flow out of the columns they flow through detectors of various kinds that assist in identifying and quantifying the compounds.
As a sample flows through an instrument such as a GC it may be exposed to various other fluids such as carrier fluids, calibration fluids and the like. Moreover, the fluid flow paths include many junctions and intersections. At each step along the processing path where fluids are rerouted or further isolated, the fluid flows through a variety of plumbing hardware and control systems.
It is obvious that in many analytical instruments that require controlled fluid flow there are numerous fluid flow paths, and complex hardware systems that include tubing, barbs, couplings, valves, sensors, pumps and regulators of various kinds. The plumbing systems in even relatively simple instruments such as some gas chromatographs can become exceedingly complicated, not to mention the complexity added by the fluid control systems.
Precision, reliability and accuracy are of course primary goals of any analytical analysis. As such, it is essential in an analytical instrument to eliminate, or at least minimize, all sources of system failure, including problems such as leaking fittings that can adversely effect the analytical processing. The complexity of the plumbing and fluid controlling hardware of many analytical instruments presents a situation that is at odds with the fundamental principles of accuracy and precision that such instruments rely upon. Accurate analytical results require accurate fluid processing, without system failures such as non-fluid-tight couplings. But every fitting, connection, interconnection and fluid-controlling device in an analytical instrument introduces a potential site for a problem such as a leak. When even a small leak occurs in a critical connection the accuracy of analytical test data is compromised. In an instrument that contains dozens of couplings and connections the opportunity for incorrectly connected fittings is multiplied many times over.
The problems described above with respect to complicated fluid connections are well known to any laboratory technician who has operated an analytical instrument such as those described. Even in the relatively idealized conditions of a modern laboratory, and even with laboratory grade instruments, plumbing problems are a constant source of trouble with analytical instruments such as GCs. As such, there is a great benefit in reducing the number and complexity of fittings in an instrument that uses fluid flow.
But the problems noted above are even more pronounced with analytical instruments that are designed for use in the field rather than in a controlled laboratory environment. There are several reasons. First, field instruments tend to be smaller since portability may be a primary goal. As the instruments get smaller so do the fittings and connections. With miniaturized hardware it is more difficult to ensure fluid-tight processing. Second, an instrument designed for use in the field is often subject to more extreme environmental conditions and rougher handling. In many respects, therefore, field units need to be even more robust than their laboratory counterparts. This can be a difficult objective when another goal in designing the unit is reduction of size.
A relatively newer type of analytical instrument is an in-situ monitoring device that is installed in place to monitor on an ongoing basis some kind of processing activity. Such devices are often designed to interface with telephony equipment for automatic transmission of analytical data and for remote access to central processing units in the instruments. These devices may be left in the field for extended periods of time, and do not have the benefit of the constant monitoring and maintenance that both laboratory and portable instruments might enjoy. In-situ instruments therefore must be extremely rugged to provide reliable data over an extended period of time.
In-situ instruments also may be placed in extreme environmental conditions that test the limits of hardware design. For instance, such devices may be subjected to wide fluctuations in ambient temperature and other extremes in weather conditions, and to harsh chemical environments. Design engineering must take these conditions into account. But in instruments that include complicated plumbing schemes it is even more difficult than in laboratories to minimize chances for leaking fittings and the accompanying errors in obtaining reliable data.
In situ monitoring and reporting of dissolved gasses in dielectric fluid blanketed electric power transformers is one example of a situation where an in situ analytical instrument is desirable, but where technical difficulties have made such instruments difficult to design. Some kinds of large electrical transformers and other electrical power transmission and processing devices utilize dielectric fluids such as transformer oil to cool and insulate the components. With respect to transformers, various operating events and conditions can cause transformer components, such as insulating paper, and the insulating oil itself to degrade. For example, incipient transformer faults such as arcing and partial discharge can lead to transformer oil breakdown. Thermal faults can cause both oil and cellulosic decomposition. Regardless of the cause of such faults, they often result in the production of contaminants such as combustible gases including low molecular weight hydrocarbons, carbon monoxide and dioxide, and other volatile compounds, which are diffused into the oil. As a result, the insulating and cooling properties of the insulating oil are altered, diminishing the transformer""s efficiency and promoting transformer failure.
The presence of so-called fault gasses in oil-blanketed transformers and other devices has well documented implications relating to the performance and operating safety of the transformer. There is a substantial body of knowledge available correlating the presence of fault gasses with certain, identified transformer conditions and faults. It is therefore beneficial to monitor the condition of dielectric fluids in equipment such as transformers in order to maximize transformer performance, while at the same time minimizing wear and tear on the transformer, and thereby minimizing maintenance costs. Thus, information relating to the presence or absence of certain fault gasses in transformer oil can lead to greatly increased efficiency in the operation of the transformer.
As noted, the presence of some fault gasses in transformers can lead to dangerous conditions. It has been well documented that the presence of some kinds of fault gasses in transformer oil can be indicative of transformer malfunctioning, such as arcing, partial or corona discharge. These conditions can cause mineral transformer oils to decompose, generating relatively large quantities of low molecular weight hydrocarbons such as methane, and some higher molecular weight gasses such as ethylene and ethane. Such compounds are highly volatile, and in some instances they may accumulate in a transformer under relatively high pressure. This is a recipe for disaster. Left undetected or uncorrected, these explosive gasses can lead to an increased rate of degradation, and even to catastrophic explosion of the transformer. Transformer failure is a significantly expensive event for an electric utility, not only in terms of down time and the costs of replacement equipment, but also in terms of the costs associated with lost power transmission. On the other hand, by closely monitoring dissolved gasses in transformer oil, the most efficient operating conditions for a given transformer can be actively monitored and the transformer load may be run at or near a maximized peak. Moreover, when dangerous operating conditions are detected the transformer can be taken off line for maintenance.
In the past there have been many attempts to solve the problems associated with transformer gas-in-oil monitoring, but none of them ideal. Some electrical utilities routinely sample transformer oil in the field, extract gas sample aliquots and return the samples to laboratories to run dissolved gas analysis, often with laboratory GCs. Sometimes portable field GCs can be used, as well. But these methods do not give real-time analysis and may result in data that is not a true measure of actual, ongoing operating conditions. Moreover, physical sampling cannot be done on a continuous, ongoing basis, and instead requires scheduled visits. Sample analysis and historical data are thus based on widely intermittent sampling protocols rather than continuous sampling. But an intermittent sampling protocol may entirely miss a substantial transient transformer fault. That is, it is unlikely that the timing of an intermittent sampling will correlate with a specific fault event. Moreover, it is well known that each transformer tends to have a unique set of operating conditions and tends to run under certain conditions unique to that transformer. In essence, each transformer has a set of normal operating conditions that are unique to that unit. Knowledge of a transformer""s normal operating conditions allows for accurate prediction and analysis of when a certain out-of-normal condition is a true fault condition or an event that might be expected. With periodic sampling it is all but impossible to develop an accurate operating profile for each transformer. One result of such difficulties in such sampling and other factors has been that, out of safety and maintenance concerns, many commercial power transformers are run at loads that are significantly less than the transformer is capable of handling. Alternately, transformers are run at loads closer to their operating maximum without sufficient information about the existence of possible dangerous conditions, which could lead to catastrophic failure. This protocol for operating transformers is inefficient, expensive and in some cases dangerous.
There have been various attempts made at developing in situ analytical instruments for continuous monitoring and analysis of dissolved gas in transformer oil. Some of these attempts have shown some promise of success. Others have not fared as well. Regardless, the in-situ analytical instruments are often subjected to extremely harsh environmental conditions. For example, power transformers may be located in areas where ambient temperatures vary from extreme cold in winter months to extreme heat in summer. Furthermore, all large transformers are prone to vibration during operation that can be significant. Such vibration on a continued basis can be very rough on equipment near the transformer. All things considered, it is very difficult to design an accurate, precise and rugged analytical instrument that can withstand these environmental conditions without repeated failures.
The problems described above with complicated plumbing, control and hardware systems are amplified many times over in the extreme conditions found at transformer locations. The extreme temperature variations can cause thermal expansion and contraction that leads to leaking fittings and other connections, and environmental vibrations can, over time, loosen fittings and damage sensitive connections.
Therefore, despite advances in the technological solutions surrounding analytical instruments designed to sample, analyze and report data from remote locations, there is a need for a fluid handling system that is rugged and redundant enough that it will function without failure and without regular maintenance. Such a fluid handling system would be advantageously and beneficially used in both field instruments and in laboratory grade instruments.
The advantages of the present invention are achieved in a first preferred embodiment of an analytical instrument such as a gas chromatograph that utilizes a ported manifold for routing and controlling fluid flow into and through the instrument. The ported manifold includes isolated fluid flow paths that eliminate plural fittings and hardware plumbing devices. The manifold is mated to a cooperatively ported collar or flange, which is designed to mate with a rotary injector valve. Fluid control apparatus such as pressure transducers, valves and pressure regulators are connected directly to the ported manifold and are fluidly connected with appropriate fluid streams in the manifold. The combination of the manifold and collar and the manner in which the collar mates with the rotary injector valve provides for a rugged and redundant fluid flow system that eliminates the vast majority of fittings normally found in analytical instruments.